Ultrafast spin currents and ferroic oxides
This PhD thesis lies at the intersection of ultrafast spintronics and the physics of spin currents on sub-picosecond timescales. Pure spin currents are currently attracting considerable attention due to their central role in the development of next-generation spintronic devices. As data consumption continues to grow exponentially, information and communication technologies must process increasingly large volumes at higher speeds, all while minimizing energy consumption. In this context, ultrafast information processing has become a major challenge.
Pure spin currents offer several decisive advantages: in addition to their dissipationless propagation, they can now be generated, transmitted, and detected on timescales of just a few hundred femtoseconds. This progress paves the way for the emergence of ultrafast spintronic components and devices operating in the terahertz range.
The aim of this thesis project is to investigate the fundamental mechanisms governing the generation and propagation of pure spin currents on picosecond and sub-picosecond timescales, with a particular focus on ferroic oxides. These materials exhibit a wide range of remarkable and tunable properties, making them ideal candidates for enabling ultrafast spin current functionalities and addressing the societal challenges of tomorrow.
The core of this thesis work will involve the implementation of time-resolved optical and magneto-optical techniques to probe the ultrafast magnetic dynamics in epitaxial thin films of ferromagnetic and antiferromagnetic oxides. The main expected outcomes include overcoming key bottlenecks: on one hand, the tunability of ultrafast spin current generation through the half-metallicity of selected ferromagnetic oxides; and on the other hand, the control of spin information propagation at terahertz frequencies in antiferromagnetic oxides.
Hemoglobin S polymerization and diffusion in different hemoglobin mixtures HbYxHbS(1-x) with Y=At, A0, F…
Sickle cell disease (SCD) is a genetic disorder of the blood, causing anemia. It results from the polymerization of a mutated hemoglobin HbS, the oxygen-carrying protein found in red blood cells (RBCs), which causes the soft cells to deform into a rigid sickle shape under certain circumstances. Because the deformed cells induced by the polymerization will clog the blood capillaries, it induces an increase in blood pressure and ultimately degeneration of the various organs. Pharmacological treatments for sickle cell anemia include hydroxyurea, a molecule that promotes the synthesis of fetal hemoglobin (HbF) which leads to a mixture of hemoglobin HbFxHbS(1-x) in the blood, with HbF partially inhibiting polymerization of HbS. Gene therapy is also used for the treatment of this disease by stimulating the production of therapeutic hemoglobin (HbAt), or normal hemoglobin (HbA0). In collaboration with the Department of Genetic Diseases of the Red Blood Cell at Henri-Mondor hospital, we propose to study the effect of the addition of different types of hemoglobin on the polymerization process as well as the kinetics of oxygen capture at RBC level. This model study is directly linked to the treatments developed to cure this disease and aim to try to better understand them from a molecular point of view.
Measuring quantum decoherence and entanglement in attosecond photoemission
The PhD project is centered on the advanced study of attosecond photoemission dynamics. The objective is to access in real time decoherence processes induced, e.g., by electron-ion quantum entanglement. To that aim, the young researcher will develop attosecond spectroscopy techniques making use of a new high repetition rate Ytterbium laser.
Detailed summary :
In recent years, there has been spectacular progress in the generation of attosecond (1 as=10-18 s) pulses, awarded the 2023 Nobel Prize [1]. These ultrashort pulses are generated from the strong nonlinear interaction of short intense laser pulses with gas jets [2]. They have opened new prospects for the exploration of matter at the electron intrinsic timescale. Attosecond spectroscopy allows studying in real time the quantum process of photoemission and shooting the 3D movie of the electron wavepacket ejection [3, 4]. However, these studies were confined to fully coherent dynamics by the lack of experimental and theoretical tools to deal with decoherence and quantum entanglement. Recently, two techniques have been proposed to perform a quantum tomography of the photoelectron in its final asymptotic state [5, 6].
The objective of the PhD project is to develop attosecond spectroscopy to access the full time evolution of decoherence and entanglement during the photoemission process. Quantum tomographic techniques will be implemented on the ATTOLab laser platform (https://iramis.cea.fr/en/lidyl/atto/attolab-platform/) using a new Ytterbium laser source. This novel laser technology is emerging, with stability 5 times higher and repetition rate 10 times higher than the current Titanium:Sapphire technology. These new capabilities represent a breakthrough for the field and allow, e.g., charged particle coincidence techniques, to study the dynamics of photoemission and quantum entanglement with unprecedented precision.
This PhD project is performed in the frame of a recently funded European Network QU-ATTO (https://quatto.eu/), providing an advanced training to 15 young researchers, and opening many opportunities of joint work with European laboratories. In particular, strong collaborations are already ongoing with the groups of Prof. Anne L’Huillier in Lund, and Prof. Giuseppe Sansone in Freiburg. Due to the Mobility Rule, candidates must not have resided (work, studies) in France for more than 12 months since August 2022.
The student will receive solid training in ultrafast optics, atomic and molecular physics, attosecond science, quantum optics, and will acquire a broad mastery of XUV and charged-particle spectroscopy techniques.
References :
[1] https://www.nobelprize.org/prizes/physics/2023/summary/
[2] Y. Mairesse, et al., Science 302, 1540 (2003)
[3] V. Gruson, et al., Science 354, 734 (2016)
[4] A. Autuori, et al., Science Advances 8, eabl7594 (2022)
[5] C. Bourassin-Bouchet, et al., Phys. Rev. X 10, 031048 (2020)
[6] H. Laurell, et al., Nature Photonics, https://doi.org/10.1038/s41566-024-01607-8 (2025)
Mesure de la réponse intra-pixel de détecteur infrarouge à base de HgCdTe avec des rayons X pour l’astrophysique
In the field of infrared astrophysics, the most commonly used photon sensors are detector arrays based on the HgCdTe absorbing material. The manufacturing of such detectors is a globally recognized expertise of CEA/Leti in Grenoble. As for the Astrophysics Department (DAp) of CEA/IRFU, it holds renowned expertise in the characterization of this type of detector. A key characteristic is the pixel spatial response (PSR), which describes the response of an individual pixel in the array to the point-like generation of carriers within the absorbing material at various locations inside the pixel. Today, this detector characteristic has become a critical parameter for instrument performance. It is particularly crucial in applications such as measuring galaxy distortion or conducting high-precision astrometry. Various methods exist to measure this quantity, including the projection of point light sources and interferometric techniques. These methods, however, are complex to implement, especially at the cryogenic operating temperatures of the detectors.
At the DAp, we propose a new method based on the use of X-ray photons to measure the PSR of infrared detectors. By interacting with the HgCdTe material, the X-ray photon generates carriers locally. These carriers then diffuse before being collected. The goal is to derive the PSR by analyzing the resulting images. We suggest a two-pronged approach that integrates both experimental methods and simulations. Data analysis methods will also be developed. Thus, the ultimate objective of this thesis is to develop a new, robust, elegant, and fast method for measuring the intra-pixel response of infrared detectors for space instrumentation. The student will be based at the DAp. This work also involves collaboration with CEA/Leti, combining the instrumental expertise of the DAp with the technological knowledge of CEA/Leti.
Development and characterization of a reliable 13.5 nm EUV OAM carrying photon beamline
The Extreme UltraViolet (EUV) photon energy range (10-100 nm) is crucial for many applications spanning from fundamental physics (attophysics, femto-magnetism) to applied domains such as lithography and nanometer scale microscopy. However, there are no natural source of light in this energy domain on Earth because photons are strongly absorbed by matter, requiring thus vacuum environment. People instead have to rely on expensive large-scale sources such as synchrotrons, free electron lasers or plasmas from large lasers. High order laser harmonic generation (HHG), discovered 30 years ago and recognized by the Nobel Prize in Physics in 2023, is a promising alternative as a laboratory scale EUV source. Based on a strongly nonlinear interaction between an ultrashort intense laser and an atomic gas, it results in the emission of EUV pulses with femto to attosecond durations, very high coherence properties and relatively large fluxes. Despite intensive research that have provided a clear understanding of the phenomenon, it has up to know been mostly limited to laboratories. Breaching the gap towards applied industry requires increasing the reliability of the beamlines, subjects to large fluctuations due to the strong nonlinearity of the mechanism, and developing tools to measure and control their properties.
CEA/LIDYL and Imagine Optic have recently joined their expertise in a join laboratory to develop a stable EUV beamline dedicated to metrology and EUV sensors. The NanoLite laboratory, hosted at CEA/LIDYL, is based on a high repetition rate compact HHG beamline providing EUV photons around 40eV. Several EUV wavefront sensors have been successfully calibrated in the past few years. However, new needs have emerged recently, resulting in the need to upgrade the beamline.
The first objective of the PhD will be to install a new HHG geometry to the beamline to enhance its overall stability and efficiency and to increase the photon energy to 92eV, a golden target for lithography. He will then implement the generation of a EUV beam carrying orbital angular momentum and will upgrade Imagine Optic’s detector to characterize its OAM content. Finally, assisted by Imagine Optic engineers, he will develop a new functionality to their wavefront sensors in order to enable large beam characterization.
Effect of water radiolysis on the hydrogen absorption flux by austenitic stainless steels in the core of a nuclear pressurized water reactor
In pressurized water nuclear reactors, the core components are exposed to both corrosion in the primary medium, pressurized water at around 150 bar and 300°C, and to neutron flux. The stainless steels in the core are damaged by a combination of neutron bombardment and corrosion. In addition, radiolysis of the water can have an impact on the mechanisms and kinetics of corrosion, the reactivity of the medium and, a priori, the mechanisms and kinetics of hydrogen absorption by these materials. This last point, which has not yet been studied, may prove problematic, as hydrogen in solid solution in steel can lead to changes in (and degradation of) the mechanical properties of the steel and induce premature cracking of the part. This highly experimental thesis will focus on the study of the impact of radiolysis phenomena on the corrosion and hydrogen uptake mechanisms of a 316L stainless steel exposed to the primary medium under irradiation. Hydrogen will be traced by deuterium, and neutron irradiation simulated by electron irradiation on particle accelerators. An existing permeation cell will be modified to allow in operando measurement by mass spectrometry of the deuterium permeation flux through a sample exposed to the simulated primary water under radiolysis conditions. The distribution of hydrogen in the material, as well as the nature of the oxide layers formed, will be analysed in detail using state-of-the-art techniques available at the CEA and in partner laboratories. The doctoral student will ultimately be required to (i) identify the mechanisms involved (corrosion and hydrogen entry), (ii) estimate their kinetics and (iii) model the evolution of hydrogen flux in the steel in connection with radiolysis activity.
Influence of ionization density in water on fluorescent solutes. Application to the detection of alpha radiation
The location and rapid identification, at a distance, of sources of alpha and beta particle emissions on surfaces or in wet cavities or solutions, in nuclear facilities undergoing decommissioning or to be cleaned up, is a real challenge.
The aim of the proposed PhD project is to develop a concept for the remote detection of fluorescence light from water radiolysis processes on molecules or nano-agents. Temporal characterization using fluorescence lifetime measurements will enable detection to be attributed to a type of radiation, depending on its linear energy transfer (LET). In the Bragg peak of alpha radiation, where the TEL is maximal, the ionization density due to this TEL influences the fluorescence lifetime. However, dose rate effects also need to be considered.
Molecules and nanoparticles that are candidates for forming fluorescent products and are sensitive to the ionization density and radicals produced in traces at very short times will be identified by guided bibliography work, then tested and compared by measurements. Spectral measurements (absorption and fluorescence) and fluorescence lifetimes of the corresponding fluorescent species will be carried out using the multi-channel (16-channel) TCSPC (Time Corelated Single Photon Counting) method. Ion beams or alpha particles from sealed sources will be used for proof-of-concept. Ion beams or alpha particles from sealed sources will be used for proof-of-concept in the CEA clean-up/dismantling program.
Covalent 2D organic nanostructures by optically controlled cross-linking of molecular self-assemblies
The self-assembly of molecules on crystalline substrates leads to non-covalent 2D structures with interesting properties for various fields such as optoelectronics and sensors. The stabilization of these 2D networks into covalent networks, while preserving these properties, is a major challenge and a topical issue. Various demonstrations show that crosslinking can be triggered by thermal processes. Photocrosslinking, on the other hand, is poorly described and the few examples that have been found involve ultra-high vacuum conditions.
Building on our previously developed know-how and the additional expertise of chemist collaborators, we therefore propose to carry out photocrosslinking of 2D networks at atmospheric pressure. We will use a model oligophenyl system that will be functionalized to allow photocrosslinking towards the production of a covalent 2D network. The resulting networks will be characterized through the correlation of optical spectroscopy and local probe microscopy to monitor and highlight photo-induced cross-linking processes at wavelength scale.
Innovative syntheses of perovzalates and rationalization of the formation mechanism by synchrotron methods
“Perovzalates” are a new family of hybrid perovskites based on oxalate, with around ten examples listed since 2019 (AILi3MII(C2O4)3, with A = K+, Rb+, Cs+, NH4+; M = Fe2+, Co2+, Ni2+). Just like conventional perovskites, they are potentially interesting for countless applications (catalysis, optics, solar etc.), presenting additional advantages linked to the oxalate anion, which allows the incorporation of larger cations than in other hybrid pervovskites, while preserving a crystal structure similar to oxide perovskites.
However, this class of new materials is still barely explored, and the syntheses far from being mastered: the few reports to date systematically produce mixtures of phases, and relate to single crystals taken from heterogeneous solutions. In this context, the major problem is to synthesize an extended class of pure perovzalates.
This thesis addresses this challenge by exploiting a property discovered in the laboratory: the crystallization of metal oxalates by co-precipitation in water passes through transient “mineral emulsions”, that is to say nano-droplets rich in reagents which separate from water. The originality of this thesis is to exploit the nanostructuring provided by these mineral emulsions, and to test in particular using nanotomographic techniques accessible in synchrotron if they make it possible to confine the cations until crystallization.
Functionalized aluminosilicate nanotubes for photocatalysis
Rising energy demand and the need to reduce the use of fossil fuels to limit global warming have created an urgent need for clean energy collection technologies. One interesting solution is to use solar energy to produce fuels. Low-cost materials such as semiconductors have been the focus of numerous studies for photocatalytic reactions. Among them, 1D nanostructures are promising because of their interesting properties (high and accessible specific surface areas, confined environments, long-distance electron transport and facilitated charge separation). Imogolite, a natural hollow nanotubes clay, belongs to this category. Its particularity does not lies in its chemical composition (Al, O and Si) but in its intrinsic curvature, which induces a permanent polarization of the wall, effectively separating photo-induced charges. Several modifications of these materials are possible (coupling with metal nanoparticles, functionalization of the internal cavity), enabling their properties to be modulated.We have demonstrated that this clay is a nanoreactor for photocatalytic reactions (H2 production and CO2 reduction) under UV illumination. In order to obtain a useful photocatalyst, it is necessary to extend photon collection into the visible range. One strategy considered is to encapsulate and covalently graft dyes acting as antennae in the cavity. The aim of this thesis is to synthesize imogolites with different internal functionalizations, to study the encapsulation and grafting of dyes into the cavity of these functionalized imogolites, and finally to study the photocatalytic properties.